Posted by: Adam Kay | January 26, 2016

From Great Green Macaws to Brown Pelicans: a (last) round of abstracts from Tortuguero National Park

Our last batch of abstracts for the 2016 Introduction to Field Ecology course in Costa Rica. This time, the students worked on projects in Tortuguero National Park, one of the most remote parks in Costa Rica (you can only get here by boat or plane). Despite its remoteness, it is the third most visited park in Costa Rica. It was tough to access pristine areas here, so students had to do their best to come up with projects on the finger of land that supports most of the tourist lodges. As always, they came up with ideas, developed the project, collected data, and summarized their results. Here are abstracts from their work:

Isn’t that bird extinct? The potential effect of the pet trade on an endangered species, the Great Green Macaw

Nick Hable, Evan Keil, Sara Osborne

12646903_10207059226670473_7854106636443133093_oTropical birds are an important component of the multi-billion dollar exotic pet trade, with 250,000 parrots exported from the tropics annually.  The endangered Great Green Macaw (Ara ambiguus) exemplifies the ecological impacts of the tropical bird trade; the population of this species has decreased 90% since the early 20th century, and it is now found in only 10% of its original range.  We examined behavioral characteristics of the Great Green Macaw at Tortuguero National Park in Costa Rica, where the species is still abundant, in order to assess the suitability of this species as a pet.  We also collected opinions by local residents and eco-tourists regarding the ethics of keeping macaws in captivity, in order to assess how living in proximity to these birds affects views on this issue.  Because captive macaws are often kept alone, we assessed how often wild Great Green Macaws are found in groups of two or more.  Over three days of observations, all 33 macaws observed were found in groups (p<0.001).  Additionally, 42% of calls received a response.  None of the ten residents interviewed felt that macaws should be kept as pets, whereas two of ten eco-tourists felt that it was acceptable to keep macaws in captivity (p=0.08, R2 = .230).  These interviews suggest that there is little support for keeping captive macaws, although this opinion seems to be held more strongly by residents.  Our behavioral observations suggest that macaws are not suited to captivity as they are naturally gregarious.  We suggest that promoting conservation through increased regulation on the exotic pet trade, in combination with habitat restoration, to protect and restore populations of the Great Green Macaw.

Do birds of a feather, actually flock together: Niche partitioning and species interaction in a tropical island marsh

Zach George, Ethan Ridgewell, Jenny Walz, Quinn Whiting

Costa Rica contains some of the most biodiverse ecosystems in the world. In this study, we explored mechanisms allowing diverse species to coexist. Niche partitioning is the process by which species divide a habitat through the use of varying microhabitats, eating different diets, and/or occupying a location at different times. Many species use niche partitioning to maintain biodiversity in constrained conditions. Tortuguero, Costa Rica contains a hyper diverse bird community, making it an optimal site to study mechanisms that help maintain diversity. This study aimed to determine how the niche is partitioned among this diverse assemblage of birds. We observed bird activity on a small island marsh saturated with different bird species to test three hypotheses: (1) different species will prefer different microhabitats within the island marsh, (2) only one species will occupy a certain microhabitat at a time, and (3) species will use different microhabitats for different purposes. For each bird observed, we recorded species type, location, time of day, and amount of time spent foraging during a five minute observational period. Results indicated that preferred locations differed among species (X2=166.5, df=32, p=0.001,). More than one species may occupy a habitat at one time, negating our second hypothesis (X2=015.8030, df=9, p=0.0001).  In fact, each microhabitat has an equal probability to contain one or more species at a time (X2=13.1562, df=9, p=0.1557). Location does have a significant effect on the average time spent foraging, where birds located in mud and water spent twice as much time foraging than birds located in grass, logs or bushes (F=11.025, df=4, p=0.0001). Though our hypothesis that only one species will occupy at a certain microhabitat at one time was rejected, resource partitioning may be occurring in a different way than spatial or temporal separation. Instead, location did have a significant effect on foraging time, suggesting that the bird species may forage at different times, or in different areas, therefore reducing interspecific competition. Differing diets may be another way these birds partition the niche, as many of the species observed prefer different food sources. A better understanding of niche partitioning in this system may help in the development of conservation strategies in the face of habitat loss caused by human development.

Energy efficiency exhibited by brown pelican (Pelecanus occidentalis) flight patterns

Brennan Arendt, Jessica Brown, Zach Mader, McKenna Reid

McKenna, Jess, Zach, and Brennan

McKenna, Jess, Zach, and Brennan

Foraging strategies can vary widely in energetic costs, ranging from sit-and-wait predators with minimal costs, to predators that expend significant energy in actively pursue prey. Among actively foraging species, behavioral modifications that reduce energy expenditures should be favored.  We examined the flight behavior of the Brown Pelican (Pelicanus occidentalis), a species known to forage over tens of kilometers, in response to wind direction and estimated wind speed. We observed brown pelicans over two days in Tortuguero Beach, Costa Rica, under a range of weather conditions, and we recorded the number of wing flaps per 30 seconds as an indicator of energy expenditure, for birds at different positions in flocks. We found no difference in number of wing flaps based on position within flocks.  However, wing flaps increased with wind speed (p<0.001), and we found a significant interaction between wind speed and wind direction relative to pelican flight on number of wing flaps (F5,88=10.21,p<0.001, r2=0.36). Specifically, wing flap frequency was low and constant across estimated wind speeds from 0-30 km per hour when pelicans were flying with or against the wind, but flapping frequency increased sharply with wind speed when pelicans were flying perpendicular to the wind.  Pelicans were frequently observed travelling in both directions along the north-south shoreline, but we observed no pelicans flying when wind was blowing from the east at  >10 kilometers per hour, suggesting that the extra energetic costs of foraging under these conditions may have exceeded benefits of foraging under these conditions. Our results are consistent with our hypothesis that this actively foraging species modifies its behavior to minimize energetic costs associated with foraging.

Almond Joy and Coco Loco: Testing the Janzen-Connell Hypothesis along the Ocean Shoreline

Katie Hoffmann, Madison Gonsior, Emma Squires-Sperling

Katie and Madison

Katie and Madison

The Costa Rican rainforest is known for its diversity of trees, insects, birds and other taxa. But why does this diversity exist? One proposed explanation is known as the Janzen-Connell hypothesis. It predicts 1) there will be more seeds closer to the base of a parent tree (due to limited seed dispersal), but 2) there will be more seed predation closer to the parent tree (due to the effects of specialized seed predators). It follows from these two predictions that seedlings will be most successful at some intermediate distance away from host trees. This necessary spacing between members of the same species provides opportunities for other species, and thus contributes to forest diversity. This hypothesis has been generally supported with tests in high-density, high-diversity forests. Here, we tested whether it would similarly apply in a low diversity environment in Tortuguero National Park on the Atlantic coast of northern Costa Rica. We studied the coconut palm (Cocos nucifera) and the almond tree (Terminalia catappa), two common species along the ocean shore. Predators of the coconut and almond seeds include insects making colonies and marks on the seeds and fungi growing within the seeds. We measured the size, total number, and number of predated seeds in the middle of the parent tree’s crown (near) and 5m outside the crown (away). As predicted by the Janzen-Connell hypothesis, seed density was significantly higher near than away from the parent tree (almond: t=-2.921, DF=14.06, P = 0.005; coconut: t=-1.921; DF=15.66, P = 0.037), and, for almond trees, likelihood of seed predation was also significantly higher near the parent tree than away from it (X2=46.995; DF=2; P < 0.001). In contrast to the Janzen Connell prediction, likelihood of seed predation did not depend on location for coconuts (X2=0.191; DF=1; P =0.6617). In addition, we found that almond (t=-2.921; DF=14.06; P=0.0056) and coconut (t=-1.921; DF=15.66; P=0.0366) seeds closer to the parent tree were smaller than those farther away, and the likelihood of predation was greater for smaller than for larger almonds (t=-1.583; DF=596.1; P=0.0570) (seed size did not affect likelihood of predation in coconuts (t=2.165; DF=23.09; P=0.9795). These results suggest that the Janzen-Connell hypothesis was generally supported for the almond tree but not for the coconut tree. The lack of support in coconuts could be due to the fact that there seeds have a very hard outer layer that prevents most seed predation. Predation plays an important role with maintaining equilibrium within the environment. If disturbed, it can lead to imbalance of the populations of many species, therefore affecting the biodiversity of an ecosystem. Understanding how predation effects seed dispersal is important for the preservation and restoration of crucial seed species that support whole ecosystems.

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